1. Technical Field of the Invention
The invention relates generally to communication systems; and, more particularly, it relates to receivers implemented within satellite communication systems.
2. Description of Related Art
For several decades, there has been a great deal of development and interest in the development of satellite communications. However, in more recent years, there has been a much more focused interest in consumer based communications that capitalize on the benefits offered by satellite communications. In order to deal with the interfacing of the various devices at the transmitter and receiver ends of a satellite based communication channel, there has been significant development to try to arrive at standards in which this interfacing is to be performed.
One such standard relates to the Digital Satellite Equipment Control (DiSEqC™—hereinafter referred to as DiSEqC) Bus. DiSEqC is an OPEN STANDARD with additions controlled by industry agreement. The DiSEqC system is a communication bus between satellite receivers and satellite peripheral equipment, using only the existing coaxial cable. DiSEqC is a common standard that has gained a great deal of acceptance for use within consumer satellite installations to replace all conventional analogue (voltage, tone or pulse width) switching and all other control wiring. In a typical DiSEqC application, a “Universal” Slave integrated circuit (IC) supports multiple applications by supporting a great deal of functionality including performing link-configuration to identify the peripheral hardware that it is controlling. Other advantages of DiSEqC include: providing a standardized digital system with non-proprietary commands, enabling enables switching in multi-satellite installations, ensuring backwards compatible with 13/18 volt and 22 kHz tone switching, offering the potential for reduced power dissipation and thus cost reduction and improved reliability, eliminating many of the switching problems caused by incompatibility of system components, and making it easier for receiver installations using device recognition via optional two-way communication.
The DiSEqC concept is based on extending the present 22 kHz tone-signaling method employed within satellite communications, thus minimizing the changes required in Tuner-receiver or Integrated Receiver Decoder (IRD) units, and simplifying backwards compatibility. However, since the full DiSEqC protocol supports a return-signaling path and multiple peripheral devices, it is necessary to more closely define the impedances (at 22 kHz) on the bus, than the simple low impedance drive (supply voltage modulation) commonly employed with the present tone method.
DiSEqC is a single master, single or multi slave system, so communications may be initiated only by the master Tuner-receiver/IRD. This avoids the need for the software in the Tuner-receiver/IRD to perform continual monitoring of the bus (by polling or interrupts) when there may be other tasks in hand. In principle, the master can transmit messages by “chopping” an existing 22 kHz tone, generated either entirely by software or with some hardware support.
The DiSEqC slave function generally will be implemented in a simple microcontroller. When this is dedicated to DiSEqC bus support it is practicable to perform not only the control functions but also the tone decoding and encoding in software, thus eliminating many of the components currently used for 22 kHz tone detection.
While there has been much development in making the DiSEqC functionality more easily implemented within satellite communication systems, there is still a great deal of room for improvement. For example, the DiSEqC digital protocol is typically implemented within software. This is a very burdensome approach, in that, a great deal of interrupts need to be serviced. In some instances, a microprocessor would need to service an interrupt at every bit. This prior art approach has required the involvement of the software within every bit.